The projects outlined in this proposal are designed to clarify the role of phospholipid exchange proteins in the lung surfactant system. This budget year our studies are to be directed at the lamb sterol model, attempting to correlate surfactant production with synthesis of phosphatidylcholine-specific exchange proteins previously characterized in sheep lung soluble fraction. The phospholipid exchange process itself is to be characterized as to specificity and kinetics by using various donor and acceptor membranes. Phospholipid exchange proteins in rat lung are also being characterized since the rat can be subjected to a variety of physiological manipulations not easily carried out with sheep.